Carnitine is a naturally occurring B vitamin-like compound found in humans and other mammals. Carnitine has many functions, but its primarily role is in the transport of fatty acids into the mitochondria. Previous research (U.S. Pat. Nos. 5,124,357 and 5,192,804) has shown that carnitine supplementation of diets increases the lean to fat ratio of pigs. Its beneficial effects of increasing carcass leanness and improving the lean to fat ratio were also shown in fish (U.S. Pat. No. 5,030,657). In addition, carnitine has been shown to improve the hatchability of eggs when fed to laying hens (U.S. Pat. No. 5,362,753).
Carnitine is synthesized in the body from two essential amino acids, protein bound lysine and methionine. The level of enzyme involved in the synthesis of carnitine is extremely low in newborn piglets (Coffey et al., Carnitine Status and Lipid Utilization in Neonatal Piglets Fed Diets Low in Carnitine, J. Nutr. 121:1047-53; 1991). The newborn piglet must quickly switch from carbohydrate transplacental nourishment to a high-fat milk based diet. Thus, during the suckling period, the neonate must quickly develop the capacity to oxidize fatty acids and ketone bodies as fuel alternatives to carbohydrates. Given the role of carnitine in the fatty acid metabolism, its availability to newborns in adequate amounts is essential (Borum, P. R., Variation in Tissue Carnitine Concentration with Age and Sex in the Rat, Biochem J. 176:677; 1978).
The primary source of carnitine in neonatal tissue, at least 2-3 days post partum, is milk (Robles-Valdez et al., Maternal Fetal Carnitine Relationships and Neonatal Ketosis in the Rat, J. Biol. Chem. 251:6007; 1976). The presence of carnitine in the milk should enhance the piglets' ability to utilize milk fat. Coffey et al. compared lipid utilization by pigs nursing from their sow with lipid utilization by pigs fed a milk replacer with or without added carnitine and found that nursing pigs were heavier than pigs fed milk replacer. However, pigs fed the milk replacer with added carnitine grew faster (day 7 to 21) than those fed the milk replacer without carnitine. Carnitine supplementation did not affect lipid or glucose status of the pig.
Other researchers have described the effect of supplemented carnitine on milk production and fatty acid metabolism. Erfle et al. (Effect of Infusion of Carnitine and Glucose on Blood Glucose, Ketones, and Free fatty Acids of Ketotic Cows, J. Dairy Sci. 54:673-80; 1971) infused carnitine into ketotic lactating dairy cows and found improved fatty acid oxidation.
As noted above, the availability of carnitine in the diet of newborn pigs is essential for efficient transition to a high-fat milk diet. However, methods for supplementing the milk diet of nursing pigs with carnitine are presently unavailable. Use of milk replacer containing carnitine as suggested for cows would not be practicable on a large commercial scale. More importantly, milk replacers do not contain all other essential components of the swine milk. There is therefore a need in the art for alternative ways for improving the performance of newborn pigs and particularly for increasing pig and litter birth and weaning weights.
Previous research has suggested that feeding L-camitine supplemented diets to sows during the last 10 days of gestation and continuing during the entire period of lactation has certain beneficial effects on litter performance. Fremaut, D. et al., Do Lactating Sows Benefit from L-Carnitine Supplementation, Varkensbedrijf, June 1993: 20-23.
Applicants have now surprisingly discovered that feeding sows a diet containing L-carnitine only during the period of gestation substantially increases litter and pig performance both at birth and at weaning. The litter and pig performance was also improved when sow diets were supplemented with carnitine during both gestation and lactation periods. However, feeding carnitine to sows substantially only during lactation was not found particularly beneficial.